Alternan

Alternan is a water-soluble glucan produced by certain lactic acid bacteria, notably Leuconostoc citreum and Leuconostoc mesenteroides, during growth on sucrose. It is a polysaccharide polymer composed of D-glucose units linked by alternating glycosidic bonds, specifically α-1,3 and α-1,6 linkages, giving the polymer its distinctive alternating structure.

Biosynthesis occurs via the enzyme alternansucrase, a glucosyltransferase that transfers glucose from sucrose to a growing glucan chain, generating alternan rather than other glucans under certain conditions. The resulting polymer has a high molecular weight and is water-soluble, with solution viscosity increasing with concentration. Its structure and solubility distinguish it from other α-glucans such as dextran or mutan.

In industry and research, alternan is explored as a thickener, stabilizer, and texturizer in foods and personal care formulations. It can contribute to viscosity, freeze–thaw stability, and mouthfeel without imparting strong sweetness. Its partially branched, irregular structure may allow gel formation under specific conditions and with certain co-formers.

Health and safety notes: as a non-digestible polysaccharide for most people, alternan can act as a dietary fiber and may be fermented by gut microbiota, offering possible prebiotic effects. Regulatory status varies by jurisdiction; in some markets it is used as a food additive or ingredient under specific approvals.

See also: dextran, mutan, levan, glucan.